Synthesis of hydrosilanes from methylchloropolysilanes

ABSTRACT

The present invention relates to a process for preparing high yields of hydrosilanes by reacting methylchloropolysilanes with hydrogen gas under pressure at a temperature of from about 25° C to about 350° C in the presence of a copper catalyst. Useful copper catalysts include copper metal, copper salts, and complexes of copper salts with organic ligands.

BACKGROUND AND DESCRIPTION OF THE PRIOR ART

Hydrogenation catalysts for polysilanes are well known in the art. Theseinclude both metals and metal salts, which are insoluble in thepolysilane reactants, and metal complexes containing organic ligands,which are soluble in the polysilane reactants. However, hydrogenationcatalysts disclosed in the prior art generally contain palladium,ruthenium, rhodium, platinum or nickel. Although copper metal, coppersalts and copper complexes are well known as catalysts for a widevariety of reactions, most of which are oxidative in nature (see L. F.Fieser and M. Fieser, Reagents For Organic Synthesis, pp. 155-170(1967)) they have not been considered to be useful as hydrogenationcatalysts unless combined with chromium.

For example, U.S. Pat. No. 3,639,105 discloses the preparation ofhydrosilanes from alkyl-substituted disilanes and halogen-substituteddisilanes by hydrogenation of the disilane at a temperature of from 25°C to 250° C in the presence of a catalyst. The catalysts useful in theprocess of that patent are Group VIII transition metal catalysts,including organophosphine complexes of those transition metals.

Another publication (see H. Gilman and G. L. Schwebke, "Advances inOrganometallic Chemistry", 1, 89 (1964)) discloses the hydrogenation ofan unusual cyclic tetraphenyltetrasilane using an initial hydrogenpressure of 800 psi and a reaction temperature of 150° C using a copperchromite catalyst. At the same reaction conditions, hexaethyldisilanefailed to cleave. No disclosure was made of the use of a copper catalystwithout chromium. The reactivity of halogen-containing polysilanes wasnot investigated.

Another publication (Chemical Abstracts, 53, 17888 (1959)) discloses thecleavage of the Si-Si bond in methylchlorodisilanes using disilanes inthe vapor phase over 5% KOH/Al₂ O₃ at 500° C to give monosilanes.

SUMMARY OF THE INVENTION

The present invention relates in part to a process for preparing highyields of hydrosilanes by reacting methylchloropolysilanes with hydrogengas under pressure at a temperature of from about 25° C to about 350° C.

The process for production of the hydrosilanes that is disclosed in thisinvention is characterized by a copper catalyst. Useful copper catalystsinclude copper metal, copper salts, and complexes of copper salts withorganic ligands.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

This invention relates to a process for preparing silanes of the formulaH_(a) Me_(x) SiCl₄₋(a+x), comprising

A. contacting

(1) a polysilane consisting of units of the formula:

    Me.sub.x Cl.sub.y Si                                       (I),

with

(2) hydrogen gas under pressure, and

B. heating the above admixture to a temperature of from about 25° C toabout 350° C, in the presence of a catalytic amount of a coppercatalyst,

wherein a is 1 to 2, x is 0 to 3, and y is 0 to 3, the sum of a and xbeing from 1 to 4, the sum of x and y being from 1 to 3; all the siliconatoms in (I) being bonded to at least one other silicon atom and all thevalences of the silicon atoms in (I) being satisfied by other siliconatoms, Cl or Me radicals, with the proviso that the polysilane containat least one Cl group.

The process of this invention is carried out by reacting (1) and (2) inthe presence of the copper catalyst at a temperature of from about 25° Cto about 350° C. However, to effect the reaction within a reasonabletime period of, for example, less than 10 hours, the preferredtemperature range is about 100° C to about 350° C. Above 350° C, coppercatalyst and/or polysilane decomposition may occur, adversely affectingthe reaction. Although initial hydrogen pressures of 100 psig or lowermay be employed according to the process of the invention, a preferredrange of initial hydrogen pressures is from about 500 psig to about 1000psig. Reaction time is generally less than 10 hours, but it may belonger if desired for some purpose. The preferred reaction time is about1 hour to about 6 hours.

The process of the invention can be carried out in the presence orabsence of a solvent. The amount of solvent employed, if used, is notcritical and the primary purpose of the solvent is to facilitatehandling of the reaction mixture. If employed, the solvents are thosewhich do not react with chlorosilanes or hydrogen (i.e., inert to thereactants employed in the invention) and can be any such solvent such aslinear, cyclic or branched-chain hydrocarbons such as pentane,2-methylpentane, hexane, cyclohexane, octane and isoctane.

The term "copper catalyst" is intended to include materials wherein theonly metal is copper, such as copper metal (e.g., copper powder), coppersalts such as copper chlorides (e.g., cuprous and cupric chloride), andcopper salts containing organic ligands such astetramethylethylenediamine copper chloride. Useful cations in the coppersalt catalysts of the invention include both Cu(I) and Cu(II), anduseful counterions include halide, oxide, sulfide, sulfate, nitrate,hexafluorophosphate, and carbonate. The preferred anion is chloride.

The term "copper catalyst" is also intended to encompass complexes ofcopper salts with organic ligands such as the product of the reaction oftwo moles of tributylphosphine with one mole of cupric chloride. Suchcomplexes are prepared by adding the organic compound (e.g.,tributylphosphine) to an alcoholic or aqueous/alcoholic solution ofcopper metal salt and isolating the product.

The amount of copper catalyst employed in the process of this inventionis not narrowly critical as long as a catalytically effective amount ispresent. For purposes of the invention, the amount of copper catalystpresent must be at least about 0.2 wt. percent based upon the weight ofthe polysilane reactant.

The hydrogen gas under pressure useful in the process of the presentinvention may be fed into the reactor in a single charge. Alternatively,a continuous feed of hydrogen under relatively low pressure (e.g., > 1atmosphere) into the reactor during the course of the reaction may bemade.

The polysilanes which are useful in the process of the present inventionare well known in the art. For example, polysilane by-products of thereaction of methyl chloride with silicon metal include Cl₂ CH₃ SiSiCH₃Cl₂, Cl₂ CH₃ SiSi(CH₃)₂ Cl, and Cl(CH₃)₂ SiSi(CH₃)₂ Cl. Also,hexachlorodisilane and octachlorotrisilane are by-products in thecommercial preparation of trichlorosilane from silicon metal andhydrogen chloride. Thus, specific examples of useful polysilanesinclude: hexachlorodisilane, 1,1-dimethyltetrachlorodisilane,1,2-dimethyltetrachlorodisilane, 1,1,2-trimethyltrichlorodisilane and1,1,2,2-tetramethyldichlorodisilane. Also useful are polymeric silaneshaving more than two silicon atoms such as,1,1,2,3-tetramethyltetrachlorotrisilane, octachlorotrisilane anddodecylchloropentasilane.

The process of the present invention involves a reaction in whichcleavage of the silicon-silicon bond in the above-mentioned polysilanestakes place to form two silicon-hydrogen bonds to produce H_(a) Me_(x)SiCl₄₋(a+x) wherein a and x are defined above.

The following examples are given by way of illustration only in order todescribe the invention in greater detail, and are not intended to limitthe scope thereof.

As used herein, "Me" denotes the methyl group, "%" denotes weightpercent, and "psig" denotes pounds per square inch gauge.

EXPERIMENTAL Preparation of Soluble Copper Catalysts

Certain of the copper catalysts useful in the process of the presentinvention, namely, those catalysts containing an organic ligand, aresoluble in the polysilane reactant mixture. These catalysts are preparedby adding the organic ligand dissolved in methanol to a methanolicsolution of a metal chloride at room temperature. Solid catalystproducts were collected by filtration. Liquid catalyst products, such asthe tributylphosphine complex of copper chloride, were obtained byremoving the solvent under vacuum.

EXAMPLE 1

Except as otherwise noted in Table I below, the following polysilanereactant charge was used in Runs 1 to 47:

    ______________________________________                                                        Weight Percent Of                                             Charge Component                                                                              Total Charge                                                  ______________________________________                                        Cl.sub.2 MeSiSiMeCl.sub.2                                                                     56.7                                                          Cl.sub.2 MeSiSiMe.sub.2 Cl                                                                    29.7                                                          ClMe.sub.2 SiSiMe.sub.2 Cl                                                                    5.2                                                           Me.sub.3 SiSiMeCl.sub.2                                                                       3.5                                                           Me.sub.3 SiSiMe.sub.2 Cl                                                                      5.4                                                           Others          3.5                                                           ______________________________________                                    

A charge of polysilanes equal to about 43 - 45 grams was introduced intoa 300 milliliter stainless steel rocking autoclave which had first beencleaned with an abrasive cleanser and wire brush and then dried andpurged with nitrogen. Next, solid or liquid catalyst was added to thepolysilane mixture, the autoclave was pressurized with hydrogen, rockingof the autoclave was begun, and heat was applied to the mixture throughan external jacket. The temperature was raised to the desired point andmaintained for the period of time shown in Table I. The autoclave wasallowed to cool sufficiently to prevent loss of volatile products,vented, and opened in order to recover the product mixture.

Using an alternative procedure when there was a ten-fold scale-up ofreactants and a 3-liter autoclave was used (see Run 17, Table I below),the product mixture was obtained from the autoclave by displacementthrough a dip tube utilizing residual internal gas pressure in theautoclave.

The product yields, expressed as weight percents based on the totalamounts of polysilane reactant charge, were determined by gaschromatography. Although not shown in the results presented in Table I,trace amounts of H₃ MeSi were observed in most of the reactions. Theresults are presented in Table I which follows.

    TABLE I      THE CATALYTIC SYNTHESIS OF HYDROSILANES FROM POLYMETHYLCHLOROSILANES     Wt-% yield monomers.sup.a    wt-% Psig  %  Hydro Wt-%.sup.d Additive No. C     atalyst Compound Catalyst H.sub.2 ° C Hr Convers. Me.sub.2     SiCl.sub.2 MeSiCl.sub.3 Me.sub.3 SiCl HMeSiCl.sub.2 HMe.sub.2 SiCl     H.sub.2      MeSiCl Total silanes residues Compound Wt-%                        1     None --  1000.sup.b 350 5.5 60 6 6  NA.sup.c 0 0 NA 12 0 48   2 None --     1000 350 1. 50 8 8 NA 4 tr.sup.e NA 20 4 30 3 None -- 1000 275 5.  5 NA     NA NA NA NA NA NA NA NA 4 (φ.sub.3 P).sub.2 PdCl.sub.2 0.3 1000 275     5. 30 1 5 NA 4 tr.sup.e NA 10 4 20 5 (φ.sub. 3 P).sub.2 PtCl.sub.2     0.35 1000 275 5 10 1 2 NA 4 1 NA 8 5 2 6 (φ.sub.3 P).sub.2      PtCl.sub.2 .sub.m 0.35 1000 350 1. 45 3 4 NA 3 tr.sup.e NA 10 3 35 7     (φ.sub.3 P).sub.3 RuCl.sub.2 0.4 1000 275 2.5 25 1 3 NA 1 tr  NA 5 1     20 8 (φ.sub.3 P).sub.2 Rh(CO)Cl 0.4 1000 275 5. 10 2 4 NA 3 1 NA 10     4 0 9 Co.sub.2 (CO).sub.3 0.8 1000 350 1. 25 5 5 NA 2 0 NA 12 2 13 10     CoS.sub.x 1.2 1000 350 1. 59 10 11 4 14 3 4 46 21 13 11 Copper chromite     0.5 1000 275 17.5 40 3 2 NA 15 3 NA 23 18 17 12 Copper chromite 0.2 1000     350 1. 70 11 6 NA 18 2 NA 37 20 33 13 Copper chromite 0.2 1000 350 16.     100  18 11 NA 32 6 NA 67 38 33 14 CuCl 1. 1000 350 1. 96 22 11 4 39 7      14 95 60 0 15.sup.b CuCl 1. 1000 355 1. 96 20 11 4 34 8 13 90 55 6     16.sup.g CuCl 1. 1000 340-60 1. 91 23 12 3 32 7 12 89 51 2 17.sup.h CuCl     1. 1000 325 2. 82 14 6 3 34 8 11 76 53 6 18 CuCl 1. 1000 350 3. 98 26 16     3 27 6 7 85 40 13 19 CuCl 1. 1000 350-75 1. 96 14 8 2 22 4 9. 59 35 37     20 Cu powder 0.44 1000 350 1. 96 15 6 3 37 8 10 79 55 17 21 Cu powder     0.11 1000 350 1. 28 6 3 1 7 1 1 19 9 9 22 CuCl 1. 1000 350 1. 88 17 9 3     34 8 11 82 53 6 AlCl.sub.3 0.33 23 CuCl 1. 1000 280 5. 24 7 1 1 12 1 2     24 15 0 AlCl.sub.3 0.33 24 CuCl 1. 1000 325 2. 98 33 9 2 27 7 11 89 45 9     AlCl.sub.3 1.3 25 CuCl 1. 1000 360 1.3 66 5 5 2 22 5 7 46 34 20 ZnCO.sub.     3 0.32 26 CuCl 1. 1000 350 1.8 54 11 8 2 6 1 1 29 8 25 ZnCO.sub.3 1.3 27     30/70 Cu/Si alloy 2.2 1000 340-60 1. 99 20 11 4 36 7 15 93 58 6 -- 28 NP     Raney Ni.sup.l 0.4 1000 350 1. 95 18 8 3 37 8 13 87 58 8 -- 29 NP Raney     Ni 0.4 1000 350 1. 97 20 9 7 33 7 15 91 55 6 Me.sub.4 Si 13. 30 Ni on     kieselguhr.sup.j 1.1 1000 350 1. 95 15 16 3 29 8 14 85 51 10 -- 31 Ni,Zr     on kieselguhr.sup.k 1.1 1000 350 1. 80 14 15 2 24 7 13 75 44 5 -- 32     (MeOCH.sub.2 CH.sub.2 OMe)NlCl.sub.2 0.7 1000 350 1. 66 12 7 2 25 5 7 58     37 8 -- 33 (Bu.sub.3 P).sub.2 PdCl.sub.2 1.  500 120 4. 49 tr 8 tr 20 tr t     r.sup.e 28 20 21 -- 34 (Bu.sub.3 P).sub.2 PdCl.sub.2 1.  600 150 6. 72 5     23 tr 17 1 tr.sup.e 46 18 26 --  35 2Bu.sub.2 P.CuCl.sub.2.sup.l 2.  500     200 4. 84 15 13 2 36 1 10 77 47 7 -- 36 2Bu.sub.2 P.CuCl.sub.2 1.  600     150 6. 84 16 12 2 43 1 12 86 56 0 -- 37 CuCl.sub.2 0.26  600 150 6. 78     16 29 1 1 0 0 47 1 31 Bu.sub.2 P 1.5 38 2φBu.sub.2 P.CuCl.sub.2 1.     600 150 6. 67 11 18 2 5 0 tr.sup.e 36 5 31 --   .sub.m 39 2φ.sub.2     P.CuCl.sub.2 1.  600 150 6. 28 1 1 tr tr 0 0 2 0 26 -- 40 (Me.sub.2     NCH.sub.2 CH.sub.2 NMe.sub.2)CuCl.sub.2 1.  600 150 22. 75 10 22 1 15 tr     1 48 16 27 -- 41 (C.sub.16 H.sub.33 NMe.sub.2).sub.2 CuCl.sub.3 1.  600     150 6 45 1 8 tr 4 0 tr 13 4 32 42 (acac).sub.2 Cu 1.  600 150 6.  4 1 1     tr 1 0 0 3 1 1 43 (Bu.sub.3 P).sub.2 NlCl.sub.2 2. 1000 200 4. 84 7 14 1     30 4 8 64 42 20 44 (Bu.sub.3 P).sub.2 NlCl.sub.2 1.  600 150 6.5 86 17     15 2 37 tr.sup.e 13 84 50 2 45 (Bu.sub.3 P).sub.2 NlCl.sub.2 1.  750 100     6.5 86 17 11 2 43 tr.sup.e 11 84 54 2 46 (Bu.sub.3 P).sub.2 NlCl.sub.2     0.5  750 100 3.0 84 16 10 2 43 2 11 84 54 0 47 (Bu.sub.3 P).sub.2     NlCl.sub.2 0.2     .sup.a The present yields are rounded to the nearest percent.     .sup.b Nitrogen pressure rather than hydrogen pressure.     .sup.c "NA" denotes "not analyzed".     .sup.d Wt. % residues = Percent of starting material converted - Percent     of total monomers obtained.     .sup.e "tr" denotes "trace" (less than 1%).     .sup.f Disilanes with all normally accompanying solids removed.     .sup.g Disilanes with abnormal amount of accompanying solids.     .sup.h Ten-fold scale up in materials and autoclave.     .sup.i Deactivated, non-pyrophoric.     .sup.j 50% Ni, Girdler Catalyst No. G-49B.     .sup.k 50% Ni, 2% Zr, Girdler Catalyst No. G-69.     .sup.l Product of 2 Bu.sub.3 P and 1 CuCl.sub.2 in methanol.     .sup.m "φ" denotes phenyl group.

The results as presented in Table I show copper to be an effectivehydrogenation catalyst in various forms, including CuCl (Runs 14 - 19),copper powder (Runs 20 - 21), CuCl in the presence of AlCl₃ (Runs 22 -24), CuCl in the presence of ZnCO₃ (Runs 25 - 26), the complex preparedfrom tributyl phosphine and copper chloride (Runs 35 - 36), and (Me₂NCH₂ CH₂ NMe₂)CuCl₂ (Run 40).

It is to be noted that high yields of hydrosilane monomers are obtainedusing 1 wt. % CuCl catalyst based on the weight of polysilane reactantat 350° C and 1000 psig with a reaction time of 1 hour (see Runs 14 - 16wherein hydrosilane monomer yields are 60%, 55%, and 51% respectively).It should also be noted that a high total yield of hydrosilane monomers(55% yield) is obtained using a very small amount of copper catalyst(0.44 wt. % of copper powder based upon the weight of the polysilanereactant - see Run 20). Moreover, Run 36 provides a high yield ofhydrosilane monomers (56%) under mild conditions (600 psig H₂, 150° C)using a small amount of copper catalyst (1 wt. % of 2Bu₃ P.CuCl₂ ≈ 0.12wt. % net copper).

It is surprising that copper provides a hydrogenation catalyst forpolysilanes that is comparable in effectiveness to that of Raney nickel-- long considered to be an excellent hydrogenation catalyst -- undersimilar reaction conditions. For example, Run 20 using 0.44 wt. % copperpowder catalyst provides the same yield of hydrosilanes as is providedin Run 29 using 0.4 wt. % Raney nickel catalyst (55% hydrosilanes) underidentical conditions.

EXAMPLE 2

The product mixture obtained using Run 17 (wherein 430 grams of adisilane mixture was reacted in a 3-liter rocking autoclave) wasdistilled to give 326 grams of a mixture of monomeric silanes, 77 gramsof a mixture of disilanes, and 2% of a residue. The recovered disilanemixture was divided into two parts. One half of the disilane mixture wasreacted with hydrogen at 1000 psig in the presence of a copper chloridecatalyst. The other half of the disilane mixture was reacted withhydrogen at 1000 psig in the presence of a Raney nickel catalyst. Adetermination was made of the extent of reaction for each catalyst andof the amount of unreacted disilane which was available for furtherreaction by recycling. The results are presented in Table II below.

                  TABLE II                                                        ______________________________________                                        Catalyst           1 wt. % CuCl                                                                             0.4 wt. % Ni                                    Reaction Temperature                                                                             325° C                                                                            350° C                                   Reaction Time      2.5 hours  1 hour                                          Weight Percent Monomer Products                                               H.sub.2 MeSiCl     3          6                                               HMe.sub.2 SiCl     3          2                                               HMeSiCl.sub.2      15         21                                              Me.sub.3 SiCl      2          2                                               MeSiCl.sub.2       8          9                                               Me.sub.2 SiCl.sub.2                                                                              6          9                                               Percent Conversion 40-50      70                                              ______________________________________                                    

EXAMPLE 3

In order to determine whether the obtaining of the products H₂ MeSiCl,MeSiCl₃, and HMeSiCl₂ was dependent upon redistribution reactions (suchas H₂ MeSiCl + MeSiCl₃ ⃡ 2 HMeSiCl₂), an experiment was carried outusing a product mixture containing 12 wt. % MeSiCl₃ (more than normallyexpected to be found in a product mixture. See Run 28 where ˜ 8 wt. %MeSiCl₃ was formed). After 1 hour at 350° C in the presence of 0.4 wt. %Raney nickel catalyst, the yield of new monomers was given in Table III.As can be seen by comparison with the results of Run 28, no substantialchange in product distribution had occurred (note especially the amountsof H₂ MeSiCl and new MeSiCl₃ formed).

                  TABLE III                                                       ______________________________________                                                   Wt. Percent Yield                                                  Monomer      Example 3    Run 28 (Table I)                                    ______________________________________                                        H.sub.2 MeSiCl                                                                             11           13                                                  Hme.sub.2 SiCl                                                                              6            8                                                  HMeSiCl.sub.2                                                                              38           37                                                  Me.sub.3 SiCl                                                                               3            3                                                  MeSiCl.sub.3  5            8                                                  Me.sub.2 SiCl.sub.2                                                                        24           18                                                  Percent conversion                                                                         96           91                                                  ______________________________________                                    

EXAMPLE 4

Fifty pounds of a mixture of polysilanes obtained as by-products of thereaction of silicon with methyl chloride and comprising 9.1 wt. percentof compounds having a boiling point of less than 149° C, 3.3 percentwith a boiling point of greater than 159° C, 4.2 percent of Me₄ Si₂ Cl₂,and 83.5 percent of a mixture of Me₃ Si₂ Cl₃ and Me₂ Si₂ Cl₄, wascharged into a 50 gallon stirred autoclave. The 2Bu₃ P.CuCl₂ catalystwas added (225 grams, 1 wt. percent), and 600 psig hydrogen pressure wasapplied at 25° C. The resulting molar ratio of H₂ : disilanes was about0.5:1. The mixture was heated to 150° C and an 800 psig pressure wasmaintained by hydrogen addition during the ensuing 6.5 hour reactionperiod. After cooling and venting, the following product mixtureresulted:

    ______________________________________                                        H.sub.2 MeSiCl     9.2 wt. %                                                  HMe.sub.2 SiCl     1.2                                                        HMeSiCl.sub.2      37.4                                                       Me.sub.3 SiCl      0.6                                                        MeSiCl.sub.3       12.8                                                       Me.sub.2 SiCl.sub.2                                                                              17.8                                                       compounds bp 71° - 149°                                                            13.4                                                       Me.sub.4 Si.sub.2 Cl.sub.2                                                                       3.6                                                        Me.sub.3 Si.sub.2 Cl.sub.3 + Me.sub.2 Si.sub.2 Cl.sub.4                                          0.8                                                        compounds bp > 159°                                                                       2.5                                                        ______________________________________                                    

EXAMPLE 5

Another reaction was performed at 1 atmosphere hydrogen pressure in theliquid phase to obtain hydrosilanes from polysilanes. A 200 milliliterflask was equipped with a magnetic stirrer, thermometer, coarsegradefilter stick, and a 6 inch Vigreaux column topped in turn by an 8 × 0.6inch tube that opened at the top to a surrounding water-jacketed spacehaving a drain line at the bottom. After flushing the flask withnitrogen and adding 1 gram of (Bu₃ P)₂.NiCl₂ to the flask, 104 grams ofthe polysilane mixture used in the Runs of Table I were charged into theflask and a hydrogen flow was begun through the filter stick at 145milliliters per minute. The mixture was heated to 90° C and maintainedin the range of 89° - 104° C for 4.5 hours, during which time 36.1 gramsof monomers were collected. There was obtained 68.5 grams of residuecomprising no more than traces of monomers and disilanes except for themainly unreacted compounds Me₂ ClSiSiClMe₂ and Me₃ SiSiClMe₂. Themonomer mixture contained the following silanes:

    ______________________________________                                        Monomer         Yield (wt. percent)                                           ______________________________________                                        H.sub.2 MeSiCl  3.9                                                           HMe.sub.2 SiCl  tr                                                            HMeSiCl.sub.2   15.5*                                                         Me.sub.3 SiCl   4.5                                                           MeSiCl.sub.3    31.7                                                          Me.sub.2 SiCl.sub.2                                                                           44.5                                                          ______________________________________                                         *Reactant contained 5.4 wt. percent HMeSiCl.sub.2                        

The reaction was repeated at 100° C and 150° C using 2 wt. percent ofthe copper catalyst. Except during an initial period when Me₃ SiSiMeCl₂was selectively consumed, no significant amount of hydrosilanes wasproduced.

EXAMPLE 6

Reactions were performed at 1 atmosphere pressure in the vapor phaseover a nickel on kieselguhr catalyst and a copper on aluminum oxide(Cu/Al₂ O₃) catalyst, and the results were compared with a standard runin the absence of a catalyst. The catalyst chips were placed in avertical, resistance heated Vycor reactor tube containing an annularthermocouple well having an effective volume of 1.4 cubic centimeter percentimeter of reactor length and activated with hydrogen at 40milliliters per minute at 500°-650°. The reaction was begun at 550° C bypumping the polysilane mixture (see Example 1 for the composition of thepolysilane mixture) at rates which provided 10 to 32 seconds contacttime, based on free volume, and at molar ratios of H₂ to disilanes of1.0 to 7.7, as determined from the gas and liquid feed rates. The rangesof molar ratios of products obtained per mole of MeSiCl₃ using thenickel catalyst were HMeSiCl₂, 0.56-0.77; HMe₂ SiCl, 0.19- 0.44; and Me₂SiCl₂, 0.71-0.83 at 74-100% conversion of the tri andtetrachlorodisilane components. Similar results were obtained using thecopper catalyst, except that more Me₂ SiCl₂ than MeSiCl₃ was obtained. Acomparison of the catalyzed reaction versus the uncatalyzed standardfollows:

    ______________________________________                                                                 Standard                                                           Ni/Kieselguhr                                                                            No Catalyst                                          ______________________________________                                        ° C      550          550                                              Contact time, seconds                                                                         17           15                                               Molar ratio of hydro-                                                                         7.7          5.0                                              gen to disilanes                                                              wt. percent yield                                                             H.sub.2 MeSiCl  4.4          1.5                                              HMe.sub.2 SiCl  7.2          9.3                                              HMeSiCl.sub.2   19.6         12.5                                             Me.sub.3 SiCl   2.4          3.8                                              MeSiCl.sub.3    33.5         27.0                                             Me.sub.2 SiCl.sub.2                                                                           21.4         30.0                                             Wt. percent unreacted                                                                         11.5         16.0                                             disilanes                                                                     Wt. percent yield hydro-                                                                      31.2         23.3                                             silanes                                                                       ______________________________________                                    

EXAMPLE 7

This experiment was carried out to determine whether a recovered liquidcatalyst concentrate could be reused effectively in a subsequentreaction. A mixture (which had previously been heated for 7 hours at100° C under 750 psig of hydrogen with only 22 wt. percent conversion ofdisilanes and formation of only 4 wt. percent monomers) of 50 grams ofpolysilane reactants (see Example 1 for the composition of thepolysilane reactants) and 1 wt. percent of 2Bu₃ P.CuCl₂ catalyst washeated at 150° C under 600 psig of hydrogen at 25° C for 6 hourswhereupon Mixture A resulted. Mixture A was then distilled at 60° C and15 millimeters of Hg along with 5 grams of the 8 grams analytical sampleremoved following the 100° C treatment. The residue was cooled undernitrogen when disilanes began to reflux in the head of the reactor. Ninegrams of combined polysilanes and catalyst was mixed with 40 grams offresh disilane mixture and treated under 600 psig of hydrogen for 6hours at 150° C. Mixture B was obtained, demonstrating that the catalystwas substantially effective upon reuse.

    ______________________________________                                                     Mixture A  Mixture B                                             ______________________________________                                        Wt. Percent H.sub.2 MeSiCl                                                                   12           12                                                 HMe.sub.2 SiCl                                                                              tr           tr                                                 HMeSiCl.sub.2 42           34                                                 Me.sub.3 SiCl  2            1                                                 MeSiCl.sub.3  12           17                                                 MeSiCl.sub.2  16           17                                                Total monomers 84           81                                                Total hydrosilanes                                                                           54           46                                                Percent conversion                                                                           86           93                                                Percent residue                                                                               2           12                                                ______________________________________                                    

What is claimed is:
 1. A process for preparing silanes of the formulaH_(a) Me_(x) SiCl₄₋(a+x), comprisingA. contacting(1) a polysilaneconsisting of units of the formula:

    Me.sub.x Cl.sub.y Si                                       (I),

with (2) hydrogen gas under pressure, and B. heating the above admixtureto a temperature of from about 25° C to about 350° C, in the presence ofa catalytic amount of a copper catalyst,wherein a is 1 to 2, x is 0 to3, and y is 0 to 3, the sum of a and x being from 1 to 4, the sum of xand y being from 1 to 3; all the silicon atoms in (I) being bonded to atleast one other silicon atom and all the valences of the silicon atomsin (I) being satisfied by other silicon atoms, Cl or Me radicals, withthe proviso that the polysilane contain at least one Cl group.
 2. Theprocess of claim 1 wherein the catalyst is copper metal.
 3. The processof claim 1 wherein the catalyst is cuprous chloride.
 4. The process ofclaim 1 wherein the catalyst is a trialkylphosphine complex of a coppersalt.
 5. The process of claim 1 wherein the catalyst is the product ofthe reaction of two moles of tributylphosphine with one mole of cupricchloride.
 6. The process of claim 1 wherein the polysilane is Cl₂ CH₃SiSiCH₃ Cl₂.
 7. The process of claim 1 wherein the polysilane is Cl₂ CH₃SiSi(CH₃)₂ Cl.
 8. The process of claim 1 wherein the polysilane isCl(CH₃)₂ SiSi(CH₃)₂ Cl.